Maybe you don't need pyenv and/or virtualenv in most cases.

Install Python

Don't have brew? Go to

brew install python3

If you still need Python 2, run brew install python.

Install Jupyter Notebook

pip3 install jupyter
python3 -m ipykernel install --user

You also want Python 2 kernel, so then:

pip install ipykernel
python -m ipykernel install --user

That's all.

How about virtualenv?

Since Python 3 got its own virtual environment tool called venv, You no longer need virtualenv itself.

If you want a virtual envs on your project, run:

python3 -m venv venv
source ./venv/bin/activate

then venv will creates virtual envs on ./venv folder on the root of your project.